The present invention relates to antennae for two-way communication and global positioning satellite systems, and more particularly to planar antennae for such applications.
Cellular telephones commonly are used for mobile communication with passengers in vehicles. Such telephones usually have a hand-held unit which includes a microphone, a small speaker and a keypad for placing calls and controlling the operation of the telephone. The hand-held unit is coupled by a cable to an electronics module that contains a radio frequency transceiver. The transceiver in turn is coupled to an antenna on the exterior of the vehicle to send and receive the radio frequency signals. Cellular telephones transmit in the 824 to 845 MHz frequency band and receive signals in the 870 to 896 MHz frequency band.
A typical cellular telephone antenna for a motor vehicle is attached to the exterior surface of a window and comprises a short section of rigid wire extending vertically from the vehicle body. A coupling box is mounted on the interior surface of the window opposite to the antenna and is connected by a coaxial cable to the transceiver. The coupling box and the antenna are electrically coupled so that signals from the transmitter section of the transceiver are applied to the exterior wire from which the signals radiate. The coupling also allows radio frequency signals to be received by the exterior element and applied to the receiver section of the transceiver.
Even though such cellular telephone antennae are relatively short, protruding approximately one foot from the surface of the vehicle, they are subject to accidental breakage and acts of vandalism. Although cellular telephone antennae are considered by some people to be a status symbol, others may consider them to be unsightly and a detraction from the aesthetic appearance of the vehicle.
U.S. Pat. No. 5,041,838 discloses a low profile, flat disk-shaped antenna for bidirectional communication, such as cellular telephones. This antenna is attached to a horizontal exterior surface of the motor vehicle, such as the roof. A coaxial cable extends through a hole in that surface, coupling the external antenna to the transceiver inside the motor vehicle.
Motor vehicles are now available with receivers for the Global Positioning System (GPS) to provide location determination and navigation. The GPS consists of twenty-four artificial earth satellites positioned in a constellation so that typically seven, but a minimum of four, satellites will be observable by a receiver anywhere on or near the earth's surface. Each GPS satellite transmits data via L-band frequency signals that allow receivers on the earth to precisely measure the distance to that satellite and thereafter to compute the user's position (longitude and latitude) and velocity to a high degree of accuracy using conventional triangulation techniques.
Heretofore separate antennae were required to be mounted on a motor vehicle for GPS, a cellular telephone or other bidirectional radio equipment. This multiple antennae arrangement often detracted from the aesthetic appearance of the motor vehicle.